Am 04.09.21 um 11:56 schrieb Antonio Quartulli:
> Do not accept handshakes with peers trying to negotiate TLS lower than 1.2.
> TLS 1.1 and 1.0 are not recommended and therefore will, by default,
> allow TLS 1.2 as minimum version.
>
> The minimum allowed version can still be controlled via
> '--tls-version-min'.
>
> At the same time automatically set '--tls-version-min' to 1.0 if the
> user requires compatibility with versions onlder than 2.3.7, as that was
> the only version supported back then.
>
> Signed-off-by: Arne Schwabe <a...@rfc2549.org>
> Signed-off-by: Antonio Quartulli <a...@unstable.cc>
> ---
> Changes.rst | 5 +++++
> doc/man-sections/generic-options.rst | 2 ++
> src/openvpn/options.c | 16 ++++++++++++++++
> 3 files changed, 23 insertions(+)
>
> diff --git a/Changes.rst b/Changes.rst
> index f803b760..472421c8 100644
> --- a/Changes.rst
> +++ b/Changes.rst
> @@ -71,6 +71,11 @@ Deprecated features
> This option mainly served a role as debug option when NCP was first
> introduced. It should now no longer be necessary.
>
> +TLS 1.0 and 1.1 are deprecated
> + ``tls-version-min`` is set to 1.2 by default. OpenVPN 2.6.0 defaults
> + to a minimum TLS version of 1.2 as TLS 1.0 and 1.1 should be generally
> + avoided. Note that OpenVPN versions older than 2.3.7 use TLS 1.0 only.
> +
> ``--cipher`` argument is no longer included in ``--data-ciphers`` by default
> Data cipher negotiation has been introduced in 2.4.0 and been
> significantly
> improved in 2.5.0. The implicit fallback to the cipher specified in
> diff --git a/doc/man-sections/generic-options.rst
> b/doc/man-sections/generic-options.rst
> index 3e099e12..e6c1fe45 100644
> --- a/doc/man-sections/generic-options.rst
> +++ b/doc/man-sections/generic-options.rst
> @@ -70,6 +70,8 @@ which mode OpenVPN is configured as.
> ``--data-ciphers``
> - 2.3.x or lower: ``--data-cipher-fallback`` is automatically added with
> the same cipher as ``--cipher``
> + - 2.3.6 or lower: ``--tls-version-min 1.0`` is added to the configuration
> + when ``--tls-version-min`` is not explicitly set.
>
> --config file
> Load additional config options from ``file`` where each line corresponds
> diff --git a/src/openvpn/options.c b/src/openvpn/options.c
> index f2fb6d64..6f6eb73d 100644
> --- a/src/openvpn/options.c
> +++ b/src/openvpn/options.c
> @@ -850,6 +850,7 @@ init_options(struct options *o, const bool init_gc)
> o->use_prediction_resistance = false;
> #endif
> o->tls_timeout = 2;
> + o->ssl_flags = (TLS_VER_1_2 << SSLF_TLS_VERSION_MIN_SHIFT);
> o->renegotiate_bytes = -1;
> o->renegotiate_seconds = 3600;
> o->renegotiate_seconds_min = -1;
> @@ -3140,6 +3141,21 @@ need_compatibility_before(const struct options *o, int
> version)
> static void
> options_set_backwards_compatible_options(struct options *o)
> {
> + /* TLS min version is not set */
> + if ((o->ssl_flags & SSLF_TLS_VERSION_MIN_MASK) == 0)
> + {
> + if (need_compatibility_before(o, 20307))
> + {
> + /* 2.3.6 and earlier have TLS 1.0 only, set minimum to TLS 1.0 */
> + o->ssl_flags = (TLS_VER_1_0 << SSLF_TLS_VERSION_MIN_SHIFT);
> + }
> + else
> + {
> + /* Use TLS 1.2 as proper default */
> + o->ssl_flags = (TLS_VER_1_2 << SSLF_TLS_VERSION_MIN_SHIFT);
> + }
> + }
> +
> /* Versions < 2.5.0 do need --cipher in the list of accepted ciphers.
> * Version 2.4 might probably does not need it but NCP was not so
> * good with 2.4 and ncp-disable might be more common on 2.4 peers.
>
Acked-By: Arne Schwabe <a...@rfc2549.org>
Note that on newer Ubuntu versions, which their strangely patched
OpenSSL, you are already getting this behaviour by default.
Arne
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